1. Field of the Invention
The present invention relates to pneumatic tires.
2. Description of the Related Art
In recent years, run flat tires that include inserts (also referred to as load support layers) inward of sidewalls have been developed, and are becoming widespread. Such run flat tires are referred to as side-reinforcing type run flat tires.
In the side-reinforcing type run flat tire, when an internal pressure is reduced due to puncture, the weight of the vehicle is supported by the inserts. This run flat tire enables running over a certain distance also in a punctured state. An Automobile having the run flat tires mounted therein need not have a spare tire on a constant basis. In a case where the run flat tire is used, change of tires in an inconvenient place can be avoided. An example of the side-reinforcing type run flat tire is disclosed in JP2005-126555.
The tire includes beads. Each bead includes a core, and an apex extending outward of the core in the radial direction. The apex is tapered outward in the radial direction, and is formed from a highly hard crosslinked rubber.
The apex is formed from a single rubber composition in general. Components contained in the rubber composition and contents of the components are adjusted to adjust a characteristic of the apex.
For example, a crosslinked rubber having a high elastic modulus may be used for the apex. The tire including the apex is excellent in steering stability. However, the apex is likely to transmit vibration caused due to unevenness of a road surface. The apex may deteriorate ride comfort exhibited by the tire.
The apex is disposed inward of an insert in the radial direction. As in the tire disclosed in JP2005-126555 described above, the insert may be joined to the apex. In this case, in a case where an internal pressure of the tire is reduced due to puncture, stress is concentrated on a boundary face between the insert and the apex. In particular, in a case where an apex having a high elastic modulus is used, the concentration of the stress becomes significant. The significant concentration of the stress affects durability (also referred to as run flat durability) of the tire in the case of an internal pressure of the tire being reduced due to puncture.
An object of the present invention is to make available a pneumatic tire excellent in ride comfort and run flat durability.